Plants acquired multicellularity, distinct from animals, and have evolved their own mechanisms to build body structures suited to a sessile lifestyle. Keys to understand plants' body building may lie in several features: flexibility of plant cell differentiation and proliferation, autonomous pattern generation, multilayered interactions, plant-unique programmed cell death, plant-specific regulatory networks of gene expression, and formation of tissues and organs characteristic of plants on these bases. For studying the molecular mechanisms of these events and phenomena, we have developed bioresources and both experimental and theoretical systems, such as temperature-sensitive mutants and many other peculiar mutants of Arabidopsis, cell and tissue cultures of Arabidopsis and Torenia, and mathematical models of pattern generation. Using these tools in combination with various methodologies, including analyses in molecular genetics, physiology, biochemistry, morphology, histology, and developmental biology, as well as CLSM imaging, transcriptomics, and computer simulation, we have been attempting to elucidate the fundamental mechanisms of plants' body building.